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NFPA CFPS Exam - Topic 6 Question 12 Discussion

Actual exam question for NFPA's CFPS exam
Question #: 12
Topic #: 6
[All CFPS Questions]

The primary mechanism by which carbon dioxide extinguishes fire is

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Suggested Answer: C

The primary mechanism by which carbon dioxide extinguishes fire is smothering, or displacing the oxygen that the fire needs to sustain combustion. Carbon dioxide is a gas that is heavier than air, so when it is released from the extinguisher, it forms a blanket over the fire and pushes away the oxygen. Without oxygen, the fire cannot continue to burn and is extinguished1234

Cooling is a secondary mechanism by which carbon dioxide extinguishes fire. Carbon dioxide is stored as a liquid under high pressure in the extinguisher, and when it is released, it expands rapidly and cools down. The cold gas absorbs heat from the fire and lowers the temperature of the fuel below its ignition point. However, cooling is not the main effect of carbon dioxide, as it is less effective than water in reducing the heat of the fire1234

Saponification and chemical inhibition are not mechanisms by which carbon dioxide extinguishes fire. Saponification is a process by which wet chemical agents react with fats and oils to form a soapy foam that seals the surface of the fire and prevents re-ignition. Chemical inhibition is a process by which dry chemical agents interfere with the chemical chain reaction of the fire and stop the production of free radicals that propagate the combustion. These mechanisms are used by other types of fire extinguishers, such as Class K and Class D extinguishers, respectively1234


Carbon Dioxide Extinguishers - University of South Carolina 4

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by Elza at Jul 06, 2025, 11:35 AM

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Jolanda
5 months ago
Chemical inhibition is also a factor, but smothering is key.
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Cherri
5 months ago
I agree, smothering is the main way it works.
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Emily
5 months ago
It's definitely smothering! CO2 displaces oxygen.
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Ashleigh
6 months ago
Wait, I thought it was cooling?
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Destiny
6 months ago
Really? I always thought it was about cooling the flames.
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Loreta
6 months ago
I feel like smothering is the right answer, but I could also see how chemical inhibition might play a role.
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Launa
6 months ago
I practiced a question like this before, and I think cooling is more related to water, not CO2.
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Julene
7 months ago
I'm not entirely sure, but I remember something about chemical inhibition being a factor too.
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Ardella
7 months ago
I think carbon dioxide works mainly by smothering the fire, cutting off the oxygen supply.
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Queenie
7 months ago
I'm a bit confused on this one. Is it possible the carbon dioxide has some kind of chemical reaction that puts out the fire? I'm not sure if I should go with cooling, smothering, or chemical inhibition.
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Gladys
7 months ago
I'm pretty confident the answer is C. Carbon dioxide cuts off the fire's air supply, which is the primary way it extinguishes the flames.
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Levi
7 months ago
Okay, let me see. I know carbon dioxide is an inert gas, so it probably works by depriving the fire of oxygen somehow. I'm going to go with C - smothering.
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Tammy
8 months ago
Hmm, I'm not sure about this one. I know carbon dioxide is used in fire extinguishers, but I can't remember the exact mechanism. I'll have to think this through carefully.
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Jarod
8 months ago
I think the answer is C - smothering. Carbon dioxide displaces oxygen and prevents the fire from getting the air it needs to keep burning.
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Tennie
10 months ago
That makes sense too, but I still think smothering is the primary mechanism.
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Christiane
10 months ago
I believe it's D) chemical inhibition, as carbon dioxide interferes with the chemical reaction of fire.
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Annette
10 months ago
I agree with Tennie, carbon dioxide smothers the fire by displacing oxygen.
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Cristina
10 months ago
Smothering, of course! Carbon dioxide is like the ultimate blanket for a misbehaving fire. Tuck it in and it's lights out.
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Linn
10 months ago
B) saponification? What is this, a cooking class? I think I'll stick to grilling, not firefighting.
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Shawna
8 months ago
C) smothering.
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Vesta
10 months ago
A) cooling.
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Tennie
10 months ago
I think the answer is C) smothering.
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Nan
11 months ago
A) cooling. Wait, is that even a thing? Someone needs to fire the exam writer, pun intended.
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Brock
11 months ago
D) chemical inhibition. Gotta love those fancy-sounding scientific terms, am I right?
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Carmela
11 months ago
C) smothering. That's the one! Carbon dioxide deprives the fire of oxygen, simple as that.
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Fabiola
9 months ago
D) chemical inhibition.
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Cruz
9 months ago
C) smothering. That's the one! Carbon dioxide deprives the fire of oxygen, simple as that.
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Jonell
10 months ago
B) saponification.
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Irma
10 months ago
A) cooling.
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